Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) can be used to set up Point-to-Multipoint (P2MP) and Multipoint-to-Multipoint (MP2MP) Label Switched Paths (LSPs). The set of LDP extensions for setting up P2MP or MP2MP LSPs may be referred to as multipoint LDP (mLDP), which may be specified in Internet Engineering Task Force (IETF) Request for Comments (RFC) 6388, titled “Label Distribution Protocol Extensions for Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths,” which is hereby incorporated by reference. Certain Upstream Label Assignment (ULA) techniques may be specified in IETF RFC 6389, titled “MPLS Upstream Label Assignment for LDP,” which is hereby incorporated by reference.
A router that experiences a node/link failure must have pre-determined alternate reroute path to protect such a failure. One approach to protect against failure of a protected node is facility protection, also known as facility backup. Facility backup methods take advantage of the MPLS label stack. Instead of creating a separate LSP for every backed-up LSP, as done in one-to-one backup methods, a single LSP is created that serves to backup one or more primary LSPs. This may also be referred to as a LSP tunnel a bypass tunnel.
Current facility backup methods distinguish incoming label map (ILM) entries using label value and context keys, supported by hardware and a forwarding plane. This can be complex and costly when new nodes are added. Principles underlying label resource occupation in facility backup label assignment include the following: (a) labels assigned by the upstream-label assigner actually occupy downstream nodes' label resources, and therefore the downstream nodes may not assign the labels to other LSPs, and (b) the upstream-label assigners may assign the upstream labels to their own upstream label switching routers (LSRs), and thus upstream label space is independent of downstream label space.